The present invention relates to a wear-resistance copper alloy for a sliding member such as a bearing and a sliding plate and, more particularly, to a wear-resistance copper alloy which exhibits excellent friction and wear properties under low-speed and high-load conditions.
The following copper alloys have conventionally been proposed: a wear-resistance copper alloy having improved wear-resistance and mechanical strength so as to be usable under high-speed and high-load conditions, produced by adding not more than 1.0 wt. % in total of at least one selected from the group consisting of Cr, Ti, V and Zr to an alloy containing 55 to 67 wt. % of Cu, 1.0 to 6.0 wt. % of Mn, 0.1 to 1.2 wt. % of Si, 0.1 to 6 wt. % of Al, 0.1 to 3.0 wt. % of Pb and the balance Zn [Japanese Patent Publication No. 44-28789 (1969)]; a wear-resistance copper alloy having an improved wear-resistance at a high temperature, produced by adding not more than 10 wt. % in total of at least one selected from the group consisting of Mn, Cr, Bi to an alloy containing 60 to 85 wt. % of Cu, 6 to 13 wt. % of Al, 3 to 20 wt. % of Ni, 1 to 10 wt. % of Co as the main ingredients [Japanese Patent Application Laid-Open No. 49-66527 (1974)]; a copper alloy for a valve seat with excellent anti-seizing property and wear-resistance at a high temperature, comprising 25 to 40% of Zn, 1 to 8% of Al, 1 to 5% of Mg, 0.3 to 2% of Si, 0.8 to 3% of Cr, 0.3 to 1% of P, not more than 5% of impurity elements and the balance Cu [Japanese Patent Publication No. 50-7010 (1975)]; a wear-resistance aluminum bronze for a sliding member having excellent cohesive wear-resistance and anti-seizing property, characterized in that the amount of iron silicate dispersed in the Cu-Al alloy is not smaller than the eutectic composition in the quasibinary phase diagram of a Cu-Al phase and an iron silicate phase [Japanese Patent Application Laid-Open No. 51-133127 (1976)]; and an age-hardening copper alloy for a bearing or a gear of a clock, which comprises 5 to 35% of Zn, 1 to 20% of Ni, more than 1 and not more than 8% of Al and the balance substantially Cu, wherein an intermetallic compound of Ni, and Al is mainly separated out by heat-treatment [Japanese Patent Publication No. 52-50724 (1977)].
As a copper alloy for a sliding member used under low-speed and high-load conditions, a high-strength brass alloy regulated by JIS H 5102, which comprises not less than 60.0 wt. % of Cu, 2.5 to 5.0 wt. % of Mn, 2.0 to 4.0 wt. % of Fe, 5.0 to 7.5 wt. % of Al, not more than 0.2 wt. % of Sn and the balance Zn, and a brass alloy regulated by ASTM B22 C 86300, which comprises 60 to 66 wt. % of Cu, 22 to 28 wt. % of Zn, 5 to 7.5 wt. % of Al, 2.5 to 5 wt. % of Mn, 2 to 4 wt. % of Fe, 1.0 wt. % of Ni, not more than 0.2 wt. % of Sn and not more than 0.2 wt. % of Pb are known.
Such a copper alloy is used for a sliding member by supplying a lubricating oil such as grease and oil to the sliding surface, or burying a solid lubricant such as graphite and molybdenum disulfide in the sliding surface or covering the sliding surface therewith.
The sliding member made of such a high-strength brass alloy is provided with a sufficient mechanical strength as a sliding member but cannot be said to have sufficient friction and wear properties. Particularly, the wear-resistance is disadvantageously lowered when the sliding member is used for a long time.
As a result of investigation and experiments of each of the ingredients of a high-strength brass alloy as a sliding material with a view to solving the above-described problem, the present inventors have found that the amount of Fe added has a great influence on the wear-resistance.
That is, in the case where the amount of Fe added is small, the wear-resistance is improved, while increase in the amount of Fe added reduces the wear-resistance.
Reduction in the amount of Fe added, however, impairs a fine alloy structure and lowers the mechanical strength of the alloy, which makes it difficult to use the alloy for a sliding member.
As a result of studies undertaken by the present inventors so as to achieve an object of providing a copper alloy which is capable of improving the wear-resistance without impairing the mechanical strength of the sliding member of a conventional high-strength brass alloy, it has been found that a copper alloy obtained by adding Cr to a composition of a conventional high-strength brass alloy in place of Fe, exhibits an excellent wear-resistance, especially, under low-speed and high-load conditions without impairing the mechanical strength as a sliding member. The present invention has been achieved on the basis of this finding.